1. Field of Invention
This invention relates to control mechanism and more particularly to a control hydraulic actuator that performs the control function by selectively positioning a piston, or other movable member, within a cylinder, and with the free end of the piston rod extending through the cylinder wall to produce the control motion. Such controls are conventionally used in aircraft and other vehicles in which jamming of the piston within the cylinder would produce control malfunction. One possible cause of piston jamming within the cylinder is the striking of the cylinder by a projectile in flight wherein the ballistic damage caused by such a projectile in striking and/or passing through the control cylinder displaces cylinder material so as to impede piston motion or cause piston jamming.
2. Description of the Prior Art
In the flight control art, attempts have been made in the past to reduce or eliminate the ballistic vulnerability of a flight control by fabricating the cylinder and/or piston as armor utilizing conventional armor-plate techniques. Such armor construction is shown in Sliney U.S. Pat. No. 3,566,741 which teaches tubular armor plate formed from an impact-resistant outer armor shell and a slightly softer inner armor shell. Such constructions proved to be unreasonably heavy and large and therefore are unacceptable for aircraft use. Further, they proved not to provide the desired ballistic-proof result.
Although not necessarily in the flight control art, the prior art is replete with patents which perform the function of armor, that is, to defeat the projectile to prevent its passing through the article. Some examples of such prior art are Jahn U.S. Pat. No. 3,977,294, Kelsy U.S. Pat. No. 3,962,976, Poole U.S. Pat. No. 4,061,815, Hoover U.S. Pat. No. 4,048,365, McArdle U.S. Pat. No. 3,924,083, Eichelberger U.S. Pat. No. 3,324,768, Burges U.S. Pat. No. 3,813,281, Dawson U.S. Pat. No. 3,826,172, VanLaetham U.S. Pat. No. 3,930,452, and Sheridan U.S. Pat. No. 2,391,535.
The U.S. Pat. No. 3,577,306 to Baker utilizes polymer laminates to prevent petaling, and this is contrary to the teaching of our invention that provides space for the petals to enter without jamming the piston.
Simmons U.S. Pat. No. 3,884,127 teaches such a control in which both the piston and the cylinder gland, through which the piston rod extends, are fabricated so as to be shearable so as to prevent piston or piston rod jamming. The Simmons patent has the disadvantage, however, that such flight controls are required to be tested to demonstrate that their structural integrity is such that they can withstand, without rupture or permanent deformation, 2.5 times the normal operating pressure which causes the piston to reciprocate within the cylinder. This test requirement dictates that the area of the piston must be at least 21/2 times the area of the cylinder gland to be able to demonstrate such structural integrity and still result in a cylinder gland which is shearable under normal operating conditions. This requirement that the piston area be at least 21/2 times the gland area results in a control of larger envelope and a greater weight than would otherwise be necessary. This envelope and weight problem is added to by the fact that larger hydraulic chambers formed by such a piston require the use of more operating fluid, with the attendant requirement for a larger fluid supply and dispensing system. In addition, such a large piston generates larger-than-normal operating forces that must be reacted by the remainder of the control system so that the remainder of the control system must be correspondingly strengthened, further increasing the weight problem. Bell U.S. Pat. No. 4,122,759 is similar to Simmons.
Wallischeck U.S. Pat. No. 4,211,151 teaches a concept of enveloping the piston rod or lining the cylinder bore of a hydraulic cylinder-piston mechanism in a control system with a sleeve of a material that is either frangible or deformable so that ballistic impact will cause disintegration or deformation thereof, and so that other deformed materials may move into the space left by the disintegrated sleeve or so that other moving parts may further displace the ballistically displaced material so as to permit the piston to continue moving within the sleeve following ballistic damage. Our invention is an improvement over Wallischeck in that it teaches a hybrid housing for the hydraulic cylinder comprising outer and inner walls with a central sleeve member positioned therebetween, each of selected material and dimension to perform the jam-proof function predictably and repeatably while utilizing minimum weight and space.